The invention relates to a process for producing a folded seam along a joint between partial cups made of sheet metal and having flanges which are so connected to form a workpiece, in particular a cup-shaped vibration damper. The invention further relates to a seaming machine for practicing the method, wherein the partial cups are placed in respective workpiece holders with their flanges pressed together and moved continuously relative to at least one folding tool.
DE-U 85 17 513 discloses that the workpiece holders holding the partial cups can be rotated around an axis running in the plane of joint. To the side of the workpiece movable seam folding robots. The workpiece elements thereof are independently powered in one direction of moving corresponding to the characteristic of the folded seam. The seaming machine has prongs and the folded seam is created in intermittent steps in that the seam folding tool is alternatingly opened, closed and laterally moved. Since the workpiece holders can be rotated, it is possible to successively produce two opposing folded seams by means of one seam folding tool. A disadvantage of this known seaming machine is the time-consuming method of operation and the consequent low productivity. Moreover, this machine permits the manufacture of only straight folded seams. In order to produce folded seams of a more complicated structure, the machine would require an additional direction of moving which in turn would involve a substantially more complex structure and control.
Moreover, it is known to produce folded seam connections of the aforesaid kind in presses where the partial cups are in fixed positions in the workpiece holders and where the seam is produced by the hammer-like use of external pressing tools. Here, the seam must be in the plane of the longest extension of the workpiece in order to advance the pressing tools. The so produced folded seam connections do not meet high quality standards since only one pressing process is possible and since a firm and tight folded seam is not possible due to the resilience of the sheet metal used for the partial cups. This problem occurs in particular during forming processes with highly resilient noble steel sheet. Moreover, there is a great amount of labor and cost involved in the manufacture of the tools which in addition are subject to high degree of wear.